Multidirectional communication system

ABSTRACT

Various of the disclosed embodiments incorporate wavelength-shifting (WLS) materials to facilitate high data rate communication. Some embodiments employ a waveguide incorporating such WLS materials to receive a wireless signal from a source. The signal may be, e.g., in the optical or ultraviolet ranges, facilitating a ˜10 Gbps data rate. Because the WLS material is sensitive in all directions, the source may be isotropic or wide-angled. The WLS material may be shaped into one or more “bands” that may cover an object, e.g., a head-mounted display. A detector may be coupled with the bands to receive the wavelength-shifted signal and to recover the original signal from the source. The WLS material may be modified to improve the waveguide retention, e.g., by incorporating layers of material having a different reflection coefficient or a Bragg reflector.

TECHNICAL FIELD

The disclosed embodiments relate to systems and materials for receptionof wireless signals.

BACKGROUND

Systems that require a high data rate connection between two devicestypically utilize a wired communication link. However, a wiredcommunication link limits the range of motion of a user in systems wheremobility is also required (e.g., in virtual or augmented realitysystems). One possible solution is to use a high data rateradio-frequency (RF) communication link. Although conventional high datarate RF communication links (e.g., IEEE 802.11ac, IEEE 802.11ad) may besuitable for some applications, virtual or augmented reality systemsoften require multi-gigabits-per-second (Gbps) links, to provide thebest viewing experience. Another possible solution is to use amulti-Gbps free-space optical communication link. However, conventionalfree-space optical communication links use a combination of optics andsmall area photodiodes as receivers, which require a very high degree ofpointing and tracking accuracy. Constraining the user or the designarchitecture to accommodate reception in such a system severely limitsthe system's flexibility.

Accordingly, there exists a need for devices capable of receiving highdata rate communications without imposing onerous restrictions on thesystem or user.

BRIEF DESCRIPTION OF THE DRAWINGS

The techniques introduced here may be better understood by referring tothe following Detailed Description in conjunction with the accompanyingdrawings, in which like reference numerals indicate identical orfunctionally similar elements:

FIG. 1A illustrates an example application of a headset for virtual oraugmented reality, in accordance with some embodiments;

FIG. 1B illustrates an example application where a user with a virtualheadset receives directional wireless data from a source in accordancewith some embodiments;

FIG. 1C illustrates an example application where a plurality of userswith virtual headsets receive wireless data from a single source ormultiple sources in accordance with some embodiments;

FIG. 1D illustrates an example application where multiple light sourcesare used as transmitters, in accordance with some embodiments;

FIG. 2 is a schematic representation of a photon entering a wavelengthshifting (WLS) material, in accordance with some embodiments;

FIG. 3 is a schematic representation of a photon entering a WLS materialincluding an additional layer with refractive index (N3) different fromthat of a core (N2) in accordance with some embodiments;

FIG. 4 is a schematic representation of a photon entering a WLS materialincluding several additional layers with different refractive indices(e.g., as a Bragg reflector) in accordance with some embodiments;

FIG. 5A is a concept form factor for a wireless receiver in accordancewith some embodiments;

FIG. 5B illustrates a combined form factor constructed by joining twoinstances of the form factor of FIG. 5A, in accordance with someembodiments;

FIG. 6A is a concept form factor for a wireless receiver, in accordancewith some embodiments;

FIG. 6B illustrates a combined form factor constructed by joining twoinstances of the form factor of FIG. 6A, in accordance with someembodiments;

FIG. 7 is a block diagram of an example receiver in accordance with someembodiments; and

FIG. 8 is a block diagram of a computer system as may be used toimplement features of some of the embodiments.

While the flow and sequence diagrams presented herein show anorganization designed to make them more comprehensible to a humanreader, those skilled in the art will appreciate that actual datastructures used to store this information may differ from what is shownin that they, for example, may be organized in a different manner, maycontain more or less information than shown, may be compressed and/orencrypted, etc.

The headings provided herein are for convenience only and do notnecessarily affect the scope or meaning of the claimed embodiments.Further, the drawings have not necessarily been drawn to scale. Forexample, the dimensions of some of the elements in the figures may beexpanded or reduced to help improve the understanding of theembodiments. Similarly, some components and/or operations may beseparated into different blocks or combined into a single block for thepurposes of discussion of some of the embodiments. Moreover, while thevarious embodiments are amenable to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and are described in detail below. Theintention, however, is not to limit the particular embodimentsdescribed. On the contrary, the embodiments are intended to cover allmodifications, equivalents, and alternatives falling within the scope ofthe disclosed embodiments as defined by the appended claims.

DETAILED DESCRIPTION

Some embodiments incorporate wavelength-shifting (WLS) materials in awireless receiver to facilitate high data rate communication. In theseembodiments, the WLS material acts as a waveguide to receive a wirelesssignal from a source and guide the received signal to a detector of thewireless receiver. For clarity, the term “wireless signal,” except whereindicated otherwise, refers herein to any photon-based electromagneticradiation signal transmitted without wires. In some embodiments, such asthe embodiments described herein, use visible wavelengths (approximately375 nanometers to 700 nanometers) or near-visible wavelengths(approximately 100 microns to 700 nanometers), radio-frequencywavelengths, microwave wavelengths, or millimeter wavelengths. Awireless signal in the visible or ultraviolet ranges may facilitate a˜10 Gbps data rate. Because the WLS material is sensitive in a largerange of incidence angles, the signal received at the WLS material isindependent of the orientation of the WLS material with respect to thesource. Additionally, the source may be isotropic or wide-angled. Insome embodiments, the WLS material is shaped into flexible sheets orbands that may conform to the shape of an object on which the WLSmaterial is to be attached. For example, the WLS material may be shapedinto one or more sheets or bands that are attached to a virtual realityhead-mounted display. A detector may be coupled with the WLS material toreceive the wavelength-shifted signal and to recover the original signalfrom the source. The WLS material may be modified to improve thewaveguide retention, e.g., by incorporating layers of material having adifferent reflection coefficient or a Bragg reflector. The wirelessreceiver and the WLS material are described in more detail below.

Although the following discussion refers to the WLS receiver beingcoupled to a head-mounted display for a virtual or augmented realitysystem, the WLS receiver may be used in other systems. For example, theWLS receiver may be used in devices coupled to other parts of the body(e.g., clothing). Similarly, the WLS receiver may be used for stationaryapplications (e.g., point-to-point communications) where the WLS ismounted on a stationary object (e.g., table-mounted, tower-mounted, orwall-mounted).

Furthermore, the term “photon” is used to refer to a photon ofelectromagnetic radiation. For example, the photon may be a photon oflight (e.g., visible or near-visible light). Similarly, the photon maybe a photon of radio-frequency, microwave, or millimeter-waveelectromagnetic radiation.

Various examples of the disclosed techniques will now be described infurther detail. The following description provides specific details fora thorough understanding and enabling description of these examples. Oneskilled in the relevant art will understand, however, that thetechniques discussed herein may be practiced without many of thesedetails. Likewise, one skilled in the relevant art will also understandthat the techniques can include many other obvious features notdescribed in detail herein. Additionally, some well-known structures orfunctions may not be shown or described in detail below so as to avoidunnecessarily obscuring the relevant description.

The terminology used below is to be interpreted in its broadestreasonable manner, even though it is being used in conjunction with adetailed description of certain specific examples of the embodiments.Indeed, certain terms may even be emphasized below; however, anyterminology intended to be interpreted in any restricted manner will beovertly and specifically defined as such in this section.

Overview—Example Applications

FIG. 1A illustrates an example application of a head-mounted display(HMD) 105 for a virtual or an augmented reality system, in accordancewith some embodiments. In some embodiments, a portion of the HMD 105includes a WLS material 110. For example, the WLS material 110 may becoupled to the surface of the HMD 105. Photons having wavelengths in afirst wavelength band that are incident on the WLS material 110 areabsorbed by the WLS material 110 and emitted as photons havingwavelengths in a second wavelength band. The photons having a wavelengthin the second wavelength band are directed (e.g., reflected internallywithin the WLS material 110) along a path 145 to a detector 140 locatedon the HMD 105. Since the WLS material 110 is able to receive photonshaving wavelengths in the first wavelength band at a large range ofincidence angles 115 a, 115 b and directs the photons having wavelengthsin the second wavelength band to the detector 140, a user wearing theHMD 105 is able to move the HMD 105 in different orientations withrespect to a transmitter of a host system while still maintaining areliable wireless signal. One will recognize that the form factordepicted herein is merely an example and that the WLS material 110 maycover a smaller or larger portion of the head mounted system or may beseparately connected (e.g., via a vest or attachment worn by the user).For example, multiple strips or bands of WLS materials 110 may becoupled to various locations on the HMD 105 (e.g., on the top, sides,and back of the HMD 105) and coupled to the detector 140. In doing so,the range of motion of the HMD 105 with respect to the transmitter ofthe host system is increased, thus allowing the user of the HMD 105 tomove more freely without losing the wireless signal. Similarly, theembodiments described herein are not restricted to head-mounted displaysand may appear on clothing, watches, accessories, vehicles, satellites,towers, etc. Furthermore, the embodiments described herein may be usedin stationary applications where the orientation of the wirelessreceiver does not change relative to the transmitter of the host system.The availability of a large area and fast detector may strongly reducethe source's pointing accuracy requirements.

FIG. 1B illustrates an example application where a user 125 a with anHMD 105 receives a directional wireless signal from a source 160. Unlikeconventional free-space optical communication links, a beam 150 ofphotons 155 does not need to be precisely aimed at a small detector onthe HMD 105. Instead, the beam 150 may be transmitted in a wider patternand still produce an adequate signal at the detector 140. The widerpattern allows the HMD 105 to move relative to the source 160 whilestill receiving an adequate signal at the detector and without requiringprecise aiming of the beam 150 at the detector 140.

FIG. 1C illustrates an example application where a plurality of users125 a, 125 b with HMDs 105 a, 105 b receive wireless data from a source135. In some embodiments, the source 135 may produce an isotropic orhemispherical distribution pattern 130. Even with such a broaddistribution pattern 130, because the WLS material 110 facilitatesphoton reception at a wide variety of incident angles, each HMD 105 a,105 b may continue to receive an adequate signal. Thus, the system maynot only be used in a single source-receiver system, but may also beused in a system where there is at least one source and multiplereceivers receiving the same signal. Data rate communications at, e.g.,optical or ultraviolet frequencies, that are higher than would bepossible at radio frequencies may be transmitted and received from awide variety of directions via various of the disclosed embodiments.

In some embodiments, the source 135 produces a directional signal toeach of the HMDs 105 a and 105 b. In these embodiments, each directionalsignal is separately addressed to either HMD 105 a or 105 b.Accordingly, each headset 105 a and 105 b may receive the same ordifferent data (e.g., a scene in a virtual world customized for eachuser 125 a and 125 b based on the position of the user 125 a and 125 bin the room and the direction that the HMDs 105 a and 105 b areoriented). Since the WLS material 110 is able to receive photons at awide variety of incident angles, the tracking requirements in order tosend the directional signal to the HMDs 105 a and 105 b may besubstantially reduced as compared to conventional free-space opticalcommunication systems.

Note that although FIG. 1C illustrates the source 135 being placed in alocation above the users 125 a and 125 b (e.g., mounted on a ceiling),the source 135 may be mounted in any location relative to the users. Forexample, the source 135 may be mounted or placed on walls, tripods,stands, shelves, tables, chairs, etc.

FIG. 1D illustrates an example application where light sources 170 and175 for lighting are used as transmitters, in accordance with someembodiments. In these embodiments, the light sources 170 and 175 are notonly used to provide lighting, but are also used to transmit photonsencoding data to a WLS receiver 190. In some embodiments, one or morewavelength bands produced by the light sources 170 and 175 are used totransmit data to the WLS receiver 190. For example, the light sources170 and 175 may produce white light, but use the blue wavelength band totransmit data to the WLS receiver 190. In some embodiments, the lightsources 170 and 175 use multiple non-overlapping wavelength bands totransmit different data streams to the WLS receiver 190.

As illustrated in FIG. 1D, the light sources 170 and 175 producedirectional beams 180 and 185, respectively that point in the directionof the WLS receiver 190. Although the directional beams 180 and 185 aredirected to the WLS receiver 190, in general, the directional beams 180and 185 may be pointed in different directions. For example, thedirectional beams 180 and 185 may be pointed at stationary WLS receiversin the room (e.g., one WLS receiver coupled to a desktop computer andanother WLS receiver coupled to a television set on the other side ofthe room). In some embodiments, the light sources 170 and 175 produceomnidirectional beams. In these embodiments, the light sources 170 and175 may broadcast the same data to multiple WLS receivers (e.g., toprovide Internet connectivity, to broadcast music or movies to devices,etc.).

In some embodiments, each light source 170 and 175 transmits data innon-overlapping wavelength bands so that multiple WLS receivers (or asingle WLS receiver that can receive data in multiple wavelength bands)may receive different data streams.

Note that although FIG. 1D illustrates the light sources 170 and 175being mounted above the WLS receiver 190 (e.g., mounted on a ceiling),the light sources 170 and 175 may be placed in other locations and/orfixtures. For example, the light sources 170 and 175 may be mounted indesktop lamps, recessed lighting fixtures, track lighting fixtures, andthe like.

Note that the discussion above illustrates only a few exampleapplications of using a WLS receiver and is not meant to limit the scopeof the disclosed embodiments to the example applications describedherein.

In some embodiments, multiple sources (e.g., the source 160, the source135, the light sources 170 and 175) are placed in multiple locations ina room (or other venue) for diversity. Doing so increases the likelihoodthat the WLS material 110 and/or the WLS receiver 190 will receivephotons from at least one source even when photons from a particularsource cannot reach the WLS material 110 and/or the WLS receiver 190(e.g., the WLS material 110 and/or the WLS receiver 190 is not facingthe general direction of the source).

Overview—Example Structure

WLS materials' wavelength-shifting properties may facilitate a materialthat is both strongly absorbing in a first wavelength band andsimultaneously non-absorbing outside of the first wavelength band suchthat the photons emitted by the WLS material are not absorbed. Variousembodiments take advantage of the WLS materials' speed of wavelengthconversion and collection efficiency to implement an improvedcommunications receiver system.

FIG. 2 is a schematic representation of a photon 205 a entering a WLSmaterial 250, in accordance with some embodiments (one will recognizethat the particulars of the quantum behavior are generalized/abstractedin this description to facilitate comprehension of the innovative higherlevel structure and application of the WLS material). The WLS material250 may be curved and/or flexible in some embodiments and may becomposed of one or more fibers. The photon 205 a may be at a wavelengthin a first wavelength band (e.g., ultraviolet or blue). The photon 205 amay enter the WLS material 250 where it may eventually encounter a WLSparticle 240 in the WLS material 250. The WLS particle 240 is configuredto absorb and emit photons having wavelengths in specified wavelengthbands. For example, the particle 240 may include dye molecules, quantumdots, lattice defects, fluorophores, and the like. In general, the WLSmaterial 250 may be a solid that includes the WLS particles 240, aliquid contained in a container (e.g., glass) that includes dissolvedWLS particles 240, or a gas contained in a vessel that includesgaseous-form WLS particles 240. In some embodiments, the WLS particle240 is resistant to ionizing radiation. In the example illustrated inFIG. 2, the WLS particle 240 is configured to absorb photons having awavelength in the first wavelength band. Accordingly, there is a highprobability that the incoming photon 205 a will be absorbed by the WLSparticle 240. The WLS particle 240 then emits one or more photons 210 ahaving wavelengths in a second wavelength band (e.g., green). Becausethe WLS particle 240 is not configured for absorption of photons havingwavelengths in the second wavelength band, the photon 210 a is unlikelyto be subsequently absorbed by the WLS material 250. Since the WLSmaterial 250 has a larger refractive index (e.g., 1.5) than thesurrounding air/vacuum, the WLS material 250 acts as a waveguide thatinternally reflects (guides, directs, or otherwise confines) the emittedphotons 210 a (when emitted at an appropriate angle). The photons 210 ainternally reflect to the detector 220.

If the photon 210 a is emitted outside an angle 235 corresponding to therefraction indices of air N1 and of the WLS material N2, the photon 210a may exit 245 the WLS material 250. However, a photon 210 a emittedwithin the angle 235 is more likely to be internally reflected 230 a,230 b, before encountering the detector 220. In some embodiments amirror 215 may be placed on the opposing end to ensure that photonsarrive at the detector 220. In some embodiments, the WLS material 250may form a “circle” and both ends 225 a and 225 b may be coupled to thedetector 220. Where the WLS material 250 is flexible, the material may“wrap around” to form, e.g., a head band or similar structure. Thus, insome embodiments, photons may be detected at either end of the WLSmaterial 250.

Regarding the speed of the wavelength conversion, since the decayprocess is an exponential process, the transfer function of thewavelength-shifting material can be modeled as a low-pass filter(strictly speaking, the process is not exactly exponential since arrivaltimes of the single photon level yields jitter, but the limit for manyphotons approaches the exponential approximation). Accordingly, the RCtime of the filter may be set by the exponential time constant of thismaterial. For example, commercially available wavelength-shiftingplastics can have a time constant of one to two nanoseconds. However, asdiscussed herein, various embodiments contemplate modifications toproduce even faster materials.

Regarding collection efficiency, since the wavelength-shifted photonsare emitted isotropically from the WLS particle 240, there is non-zeroprobability that the photons are being captured. This probability may bedetermined by the critical angle for total internal reflection. Manypresent-day materials have low capture efficiencies of approximately 5%per direction.

FIG. 3 is a schematic representation of the photon 205 a entering a WLSmaterial 250 including an additional layer with a refractive index N3305, in accordance with some embodiments. Different indices N1 and N2may suffice to produce an angle 235 at which emitted photons 210 a areinternally reflected. By applying an additional layer 305 having indexof refraction N3, the photons 205 b may enter the WLS material 250 viarelative indices N1-N3 and N3-N2 and then have corresponding emittedphotons 210 a internally reflected via N2-N3. This may have the effectof broadening the angle for internal reflection to angle 310, with theconsequence that a greater number of photons arrive at the detector 220.Additionally, the refractive indices of these layers can be configuredto act as an interference filter rejecting undesired frequencies ofphoton 205 a.

FIG. 4 is a schematic representation of a photon entering a WLS material250 including several additional index of refraction layers (e.g., as aBragg reflector) in cladding 405, in accordance with some embodiments.This structure may be used to reject incident photons of particularwavelengths and to tailor the wavelength bands of photons that areconfined within the WLS material 250. Accordingly, the remission angle410 is broadened so that even more photons 210 a are able to reachdetector 220. Thus, the additional index of refraction layers in thecladding 405 may facilitate the use of multiple wavelengths. In someembodiments, the layers may be selected such that the reflectiveproperties of different waveguides do not overlap, thereby narrowing theeffective absorption/emission of the material and enabling wavelengthdivision multiplexing with a single type of WLS material. Additionalintermediate layers having other indices of refraction may be applied.The total internal reflection may be tailored to drastically improve theefficiency, e.g., up to several tens of percent. Note, however, that asthe capture angle increases, the pulse spreading may also be increased(photons emitted at zero degrees arrive earlier than those emitted at alarger angle).

Some embodiments use WLS materials modified to provide faster absorptionand re-emission times. For example, some embodiments may incorporate dyemolecules, which can have fluorescence lifetimes down to 0.1 nanosecondor lower and may be tailored for many different wavelengths.

In some embodiments, the WLS material is tailored to enhance theemission of the WLS material, for example by imposing a periodiclongitudinal variation in refractive index such as in a fiber Bragggrating. Doing so enhances the emission of the photons in thelongitudinal direction, thereby reducing the angular spread of theemitted photons. This may be more favorable than using the additionalindex of refraction layers in the cladding 405, since it does not createpulse spreading and reduces the numerical aperture (NA) of the lightemitted from the WLS material. A smaller NA enables the focusing photonson a smaller and therefore faster detector.

Example WLS Receiver Form Factors

FIG. 5A is a concept form factor for a WLS receiver 505, in accordancewith some embodiments. As discussed, a photon 510 a having a wavelengthin a first wavelength band may be absorbed 515 in a WLS material. Aphoton 510 b having a wavelength in a second wavelength band is emitted.A tapered waveguide 520 may be used to direct the photon 510 b to across-section 525 of the same area. A focusing element 530 may thenfocus the light, e.g., on a small area detector. In some embodiments,the focusing element includes a lens. In some embodiments, the focusingelement includes a compound parabolic concentrator (CPC). In someembodiments, the focusing element includes another WLS materialconfigured to absorb photons having wavelengths in the second wavelengthband and emit photons in a third wavelength band. In these embodiments,the detector is configured to detect the photons having wavelengths inthe third wavelength band. Note that in these embodiments, the WLSmaterial may be configured to absorb and emit photons having wavelengthsin multiple different (non-overlapping) wavelength bands. For example,the WLS material may include one or more types of WLS particles.

A reflective surface or second detector may be positioned at an edge535. Alternatively, the edge 535 may be joined with a copy of thedetector (making edge 535 contiguous) to form a combined structure. Forexample, FIG. 5B illustrates a combined form factor 540 constructed byjoining two instances of the form factor 505 of FIG. 5A. Photonsincident on the WLS material can then be detected at either of thedetectors coupled with focusing elements 530 a or 530 b.

FIG. 6A is a concept form factor 635 for a WLS receiver in accordancewith some embodiments. Again, a photon 610 a having a wavelength in afirst wavelength band may be absorbed by a WLS particle 615 in a WLSmaterial 605. A photon 610 b having a wavelength in a second wavelengthband is emitted. The photon 610 b may be guided (e.g., reflected ordirected) in the WLS material 605 to a WLS material 620. The WLSmaterial 620 may emit a photon 610 c having a wavelength in a thirdwavelength band and guide the photon 610 c to a detector 625 that isconfigured to detect photons having wavelengths in the third wavelengthband. In these embodiments, the WLS material 620 acts as a focusingelement to focus (direct or guide) the emitted photons to the detector.FIG. 6B illustrates a combined form factor 640 constructed by joiningtwo instances of the form factor of FIG. 6A. The photons having awavelength in the third wavelength band may be detected at the output ofeither WLS material 640 a or WLS material 640 b. In some embodiments,the WLS material lines the perimeter of the combined form factor 640. Insome embodiments, the WLS receiver is circular and the WLS materiallines the circumference of the WLS receiver. In these embodiments, theWLS material forms a shape that directs the photons having a wavelengthin the third wavelength band to a detector. For example, the WLSmaterial may be shaped to resemble the number six (i.e., “6”) such thatthe photons travel from the circular WLS receiver (e.g., inside the loopof the number six) to the detector (e.g., at the “top” end of the numbersix) without encountering sharp bends.

Additional Contemplated Applications and Form Factors

In some embodiments, the plastic films of the WLS material may be verythin (e.g., hundreds of microns). This may permit the films to be madeinto foldable or flexible receivers. Such receivers may be used forsatellite communications where space is at a premium. For example, thesatellite may store a large unfoldable receiver such that the capturearea can be much larger than the satellite size itself.

WLS materials may also be used in receivers as part of a hybrid link.For example, the WLS material may be part of an omnidirectional opticalreceiver combined with a conventional high data rate RF communicationtransmitter (e.g., IEEE 802.11ac, IEEE 802.11ad). This may be the casein virtual or augmented reality applications (or any streaming video)where an asymmetric link is typical.

Some embodiments use WLS materials in the visible or near-visible lightwavelength bands. Some embodiments use WLS materials in radio-frequencywavelength bands. In these embodiments, the WLS material may be part ofan omnidirectional antenna with an efficiency set by theabsorption/re-emission process and its size. Some embodiments use WLSmaterials in the microwave wavelength or millimeter wavelength bands.

In some embodiments, the WLS receiver described herein is used inconjunction with a radio-frequency transmitter. In these embodiments, aclient device that includes the WLS receiver may receive data encoded inelectromagnetic radiation that is received from a host system (asdescribed herein) and transmit data back to the host system using theradio-frequency transmitter. Accordingly, the WLS receiver receives highdata rate data from the host system but transmits lower data rate databack to the host system. For example, in a virtual reality system, thehost system may transmit, to the WLS material coupled to an HMD, highdata rate video and audio data to be rendered in the HMD. The HMD maythen transmit lower data rate HMD orientation data and/or user inputdata back to the host system using the radio-frequency transmitter.

For an outdoor link, atmospheric turbulence can be a significant sourceof degradation and often limits the performance of an opticalcommunication system. The dominant effects of atmospheric turbulence onan optical signal are: frequency non-selective slow fading, limitedseeing, and beam spreading and beam wander. The use of a WLS material(e.g., as described herein) as an alternative to traditional optics forthe collecting aperture of a receiver in a turbulent channel has severaladvantages. As with other applications, the omnidirectional receptionproperties of the material obviate the need for a pointing and trackingsystem, which in this case is used to track the beam wander. Inaddition, when the aperture size is greater than the transversecoherence length of the channel, multiple spatial modes are incident onthe WLS material, resulting in emission of photons with a longerwavelength, some percentage of which have an incidence angle with thecladding that allows them to be reflected by the cladding and thenpropagate along the waveguide. This removes all spatial and phaseproperties of the incident-received spatial modes and gives rise to anumber of distinct non-coherent modes. For intensity modulatedsignaling, this results in a reduction in the severity of the frequencynon-selective slow fading by reducing the variance of the receivedintensity and is known as aperture averaging. Compared to apertureaveraging using traditional optics, this form of aperture averagingresults in an additional detection efficiency loss; however, the spotsize on the detector is now independent of the transverse coherencelength (the amount of turbulence), and for high turbulence, it may allowthe use of smaller (faster) detectors when lens speed is limited.

Example WLS Receiver

FIG. 7 is a block diagram of an example WLS receiver, in accordance withsome embodiments. A WLS material 710 absorbs a photon 705 having awavelength in a first wavelength band and emits one or more photonshaving a wavelength in a second wavelength band. A compound parabolicconcentrator (CPC) 715 focuses (and/or otherwise directs) the photonshaving a wavelength in the second wavelength band to a detector 720.Note that, as described herein, other focusing elements may be used inplace of the CPC 715. The output of the detector 720 is coupled to atransimpedance amplifier (TIA) 725 that converts a current signalproduced by the detector 720 into a voltage. From this point on, thereceiver resembles a standard receiver topology. For example, the outputof the TIA 725 is processed by components in a physical layer (PHY) chip730 (which includes an analog-to-digital converter (ADC) 735, ademodulator 740, and a channel FEC decoder 745) and a media accesscontrol (MAC) device 750 (which may include a data link layer component755). The output of the MAC device 750 is one or more data frames 760.

Computer System

FIG. 8 is a block diagram of a computer system that may be used toimplement features of some of the embodiments. The computing system 800may include one or more central processing units (“processors”) 805,memory 810, input/output devices 825 (e.g., keyboard and pointingdevices, display devices), storage devices 820 (e.g., disk drives), andnetwork adapters 830 (e.g., network interfaces) that are connected to aninterconnect 815. The interconnect 815 is illustrated as an abstractionthat represents any one or more separate physical buses, point-to-pointconnections, or both connected by appropriate bridges, adapters, orcontrollers. The interconnect 815, therefore, may include, for example,a system bus, a Peripheral Component Interconnect (PCI) bus orPCI-Express bus, a HyperTransport or industry standard architecture(ISA) bus, a small computer system interface (SCSI) bus, a universalserial bus (USB) (e.g., USB 3.1, USB Type-C, etc.), DisplayPort (e.g.,DisplayPort 1.2, DisplayPort 1.3, etc.), IIC (I2C) bus, aHigh-Definition Multimedia Interface (HDMI) 2.0 bus, or an Institute ofElectrical and Electronics Engineers (IEEE) standard 1394 bus, alsocalled “Firewire.”

The memory 810 and storage devices 820 are computer-readable storagemedia that may store instructions that implement at least portions ofthe various embodiments. In addition, the data structures and messagestructures may be stored or transmitted via a data transmission medium,e.g., a signal on a communications link. Various communications linksmay be used, e.g., the Internet, a local area network, a wide areanetwork, or a point-to-point dial-up connection. Thus, computer-readablemedia can include computer-readable storage media (e.g.,“non-transitory” media) and computer-readable transmission media.

The instructions stored in memory 810 can be implemented as softwareand/or firmware to program the processor(s) 805 to carry out the actionsdescribed above. In some embodiments, such software or firmware may beinitially provided to the processors 805 by downloading it from a remotesystem through the computing system 800 (e.g., via network adapter 830).

The various embodiments introduced herein can be implemented by, forexample, programmable circuitry (e.g., one or more microprocessors)programmed with software and/or firmware, or entirely in special-purposehardwired (non-programmable) circuitry, or in a combination of suchforms. Special-purpose hardwired circuitry may be in the form of, forexample, one or more ASICs, PLDs, FPGAs, etc.

Remarks

The above description and drawings are illustrative and are not to beconstrued as limiting. Numerous specific details are described toprovide a thorough understanding of the disclosure. However, in certaininstances, well-known details are not described in order to avoidobscuring the description. Further, various modifications may be madewithout deviating from the scope of the embodiments. Accordingly, theembodiments are not limited except as by the appended claims.

Reference in this specification to “one embodiment” or “an embodiment”means that a particular feature, structure, or characteristic describedin connection with the embodiment is included in at least one embodimentof the disclosure. The appearances of the phrase “in one embodiment” invarious places in the specification are not necessarily all referring tothe same embodiment, nor are separate or alternative embodimentsmutually exclusive of other embodiments. Moreover, various features aredescribed which may be exhibited by some embodiments and not by others.Similarly, various requirements are described which may be requirementsfor some embodiments but not for other embodiments.

The terms used in this specification generally have their ordinarymeanings in the art, within the context of the disclosure and in thespecific context where each term is used. Certain terms that are used todescribe the disclosure are discussed below, or elsewhere in thespecification, to provide additional guidance to the practitionerregarding the description of the disclosure. For convenience, certainterms may be highlighted, for example using italics and/or quotationmarks. The use of highlighting has no influence on the scope and meaningof a term; the scope and meaning of a term is the same, in the samecontext, whether or not it is highlighted. It will be appreciated thatthe same thing can be said in more than one way. One will recognize that“memory” is one form of a “storage” and that the terms may on occasionbe used interchangeably.

Consequently, alternative language and synonyms may be used for any oneor more of the terms discussed herein, nor is any special significanceto be placed upon whether or not a term is elaborated or discussedherein. Synonyms for certain terms are provided. A recital of one ormore synonyms does not exclude the use of other synonyms. The use ofexamples anywhere in this specification, including examples of any termdiscussed herein, is illustrative only and is not intended to furtherlimit the scope and meaning of the disclosure or of any exemplifiedterm. Likewise, the disclosure is not limited to various embodimentsgiven in this specification.

Without intent to further limit the scope of the disclosure, examples ofinstruments, apparatuses, methods, and their related results accordingto the embodiments of the present disclosure are given above. Note thattitles or subtitles may be used in the examples for convenience of areader, but in no way should they limit the scope of the disclosure.Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this disclosure pertains. In the case of conflict, thepresent document, including definitions, will control.

What is claimed is:
 1. A system comprising: a wireless receiver,comprising: a wavelength-shifting (WLS) material configured to: absorbelectromagnetic radiation in a first wavelength band transmitted from ahost system; emit electromagnetic radiation in a second wavelength band;and confine the electromagnetic radiation in the second wavelength bandto travel within the WLS material; a detector coupled to the WLSmaterial and configured to: detect the electromagnetic radiation in thesecond wavelength band; and produce first signals in response todetected electromagnetic radiation; and a signal processor coupled tothe detector and configured to produce second signals from the firstsignals produced by the detector.
 2. The system of claim 1, wherein theelectromagnetic radiation comprises wavelengths in the visible ornear-visible light bands.
 3. The system of claim 1, wherein theelectromagnetic radiation comprises wavelengths in the radio-frequencyband, microwave band, or millimeter-wave band.
 4. The system of claim 1,wherein the wireless receiver is coupled to an object that movesrelative to the host system.
 5. The system of claim 4, wherein theobject is a head-mounted display for a virtual or augmented realitysystem.
 6. The system of claim 1, wherein the WLS material is coupled toan object that is stationary with respect to the host system.
 7. Thesystem of claim 1, wherein the wireless receiver further comprises areflector coupled to the WLS material.
 8. The system of claim 7, whereinthe reflector is coupled to the WLS material at an end opposite to thedetector.
 9. The system of claim 7, wherein the reflector is included ina cladding for the WLS material, wherein the cladding comprises one ormore materials having specified indices of refraction that allowelectromagnetic radiation in the first wavelength band to pass throughthe cladding but that prevents electromagnetic radiation in the secondwavelength band from leaving the cladding.
 10. The system of claim 9,wherein electromagnetic radiation in a first wavelength band passesthrough the cladding and wherein electromagnetic radiation outside ofthe first wavelength band does not pass through the cladding.
 11. Thesystem of claim 7, wherein the reflector is a Bragg reflector within theWLS material and wherein the Bragg reflector enhances emissions ofelectromagnetic radiation in the second wavelength band in a specifieddirection in the WLS material.
 12. The system of claim 1, wherein theWLS material comprises a plurality of fibers.
 13. The system of claim 1,wherein the WLS material comprises a plurality of WLS particles havingdifferent absorption and emission wavelength bands.
 14. The system ofclaim 1, wherein the wireless receiver includes a plurality of WLSlayers, wherein each WLS layer absorbs and emits electromagneticradiation in non-overlapping wavelength bands.
 15. The system of claim1, wherein the wireless receiver further comprises: a focusing element,wherein an input of the focusing element is coupled to the WLS materialand an output of the focusing element is coupled to the detector,wherein the focusing element is configured to focus the electromagneticradiation emitted in the second wavelength band to the detector.
 16. Thesystem of claim 15, wherein the focusing element includes a compoundparabolic concentrator.
 17. The system of claim 15, wherein the focusingelement includes another WLS material configured to absorbelectromagnetic radiation in the second wavelength band and emitelectromagnetic radiation in a third wavelength band, and wherein thedetector is configured to detect the electromagnetic radiation in thethird wavelength band.
 18. The system of claim 15, wherein the focusingelement includes a lens.
 19. The system of claim 1, further comprising aradio-frequency transmitter configured to transmit data to aradio-frequency receiver of the host system.
 20. A processor-implementedmethod for wireless communications, comprising: absorbing, by awavelength-shifting (WLS) material of a wireless communication device,electromagnetic radiation in a first wavelength band transmitted from ahost system; emitting, by the WLS material, electromagnetic radiation ina second wavelength band corresponding to the absorbed electromagneticradiation in the first wavelength band; detecting, by a detector of thewireless communication device, the electromagnetic radiation in thesecond wavelength band; producing, by the detector, first signals inresponse to detected electromagnetic radiation; and producing, by asignal processor of the wireless communication device, second signalsfrom the first signals produced by the detector.
 21. Theprocessor-implemented method of claim 20, wherein the WLS material isconfigured to confine the electromagnetic radiation in the secondwavelength band to travel within the WLS material.
 22. Theprocessor-implemented method of claim 21, further comprisingtransmitting, by a radio-frequency transmitter of the wirelesscommunication device, data to a radio-frequency receiver of the hostsystem.